The inventor proposed in Japanese Patent Application No. 60-192863 (published under No. 62-54097 on Mar. 9, 1987) an electrodeposition coating system which includes a trolley conveyor and tanks supported on vertically extensible lifts. The trolley conveyor comprises first to fifth rails connected to one another. The first rail is straight. The second rail is curved from a lower left to an upper right. The third, or central rail is straight. The fourth rail is curved from an upper left to a lower right. The fifth rail is straight. The central rail is located in a higher position than the other rails. Each rail is a single continuous rigid rail with an inner space extending along the rail, with a generally inverted U-shaped vertical cross section, with opposed open ends, with a pair of laterally opposed bottom portions, and with a bottom space located between the opposed bottom portions. The rails provide a single continuous inner, or path, together. A roller chain is passed through the continuous inner path, and is supported on the bottom portions of the rails at its rollers. Hangers are suspended from the roller chain through the opposed bottom spaces. Works to be electrodeposition coated are hung from the hangers. All the rails are fixed rails. Thus, the trolley conveyor is a fixed one. The roller chain is moved intermittently. The tanks are located directly below the central rail. When the roller chain is stopped, the lifts are extended to move the tanks upward. Thus, the tanks accommodate the works hung from the hangers, so that the works are immersed in liquids filled into the tanks for a required period of time. Then, the lifts are retracted. Then, the roller chain is restarted. When each work has come to a position directly above the next tank, the roller chain is stopped again. Then, the lifts are extended again so that each work is accommodated in the next tank. Thus, with such a prior art, the tanks are raised after each intermittent movement of the roller chain.
However, the act of raising heavy objects, i.e., the tanks containing necessary liquids for the electrodeposition coating of works, is not of advantage to an efficient coating operation. If it is possible to move the central rail vertically, the coating operation may be made more efficiently since it is not necessary to move the tanks vertically. Since the works hung from the hangers are relatively small and lightweight objects, the central rail may be moved vertically with a smaller energy than the tanks. Thus, a technique for moving the central rail vertically has been desired. The inventor has developed such a technique. The technique resides in using a "flexible" rail.